Begonia grandis has been around in nurseries and gardens for many moons. Each time I take this old standby out of the inventory, thinking everyone has the plant, I receive requests. So, hardy begonia is once again available.
For those of you not familiar with hardy begonia, expect a plant
that grows well in open shade to a height of about two feet. The stems and
foliage have a succulent appearance, with individual leaves having heavy
substance. Each deep green leaf matures around seven inches across and nine
inches, or more, long. The outline resembles a heart with deckled edges. The
top of each leaf has a splash of deep red at the center radiating outward
along the veins, but the back side of the foliage will be all red with
prominent veins of deeper red resembling an angle-wing begonia. Each stem is
yellowish with a touch of red and red at the base near each leaf. Immature
leaves are golden-bronze with red veins. The plant is primarily grown for
the dramatic red-backed foliage. When placed so that light is behind it,
each leaf becomes transparent, glowing in golden-green reds like embers in a
low fire.
Foliage does not break dormancy and emerge until fairly late in the season, so you may want to mark your transplant to prevent disturbance. Emerging and filling out in June, in July the plants completely mature in size; blooming by the first of August. Blooms are typically small, shell pink in color, and not super showy.
When dormant the plant is a small tuber a bit larger than your thumb growing close to the surface. Once mature they produce some seed, but their main method of propagation is small tubers that form in each leaf junction. When mature, tiny tubers drop to the soil and a new plant is formed so that in time a colony or drift is formed.
Begonia grandis needs a well drained soil so it can stay relatively dry in winter while dormant. A light mulch of chopped leaves or something similar is very helpful to ensure not only a touch of added protection from cold, but a bed for the new tubers formed each fall.
Since hardy begonia breaks dormancy so late I like to pair it up with an early bloomer and something late performing in the season. I especially like to use Arum italicum for it is a bit backward in growth habit. It emerges in September filling out its bright green arrowhead shaped leaves all winter. It blooms in May, sets large bright-orange seeds in July just as the begonia is fully filled out for the season. To follow up into frost I like to use the white variegated toadlily (Tricyrtis hirta variegata) with its neat arching foliage and orchid-like blooms from September through frost. When all is killed back by approaching winter the arum will be completing a twelve month cycle in the garden.